Production of low carbon footprint magnesia

Abstract

A process for producing magnesia can include contacting CO2-containing emissions with a magnesium-containing material to produce magnesium carbonate; subjecting the magnesium carbonate to calcination to produce a CO2 by-product and magnesia; and recycling at least a portion of the CO2 by-product for contacting the magnesium-containing material to produce the magnesium carbonate. The magnesium-containing material can include mining residues, such as phyllosilicate or chrysotile mining residue, and the magnesium carbonate produced can include precipitated nesquehonite that is subjected to calcination to produce the magnesia.

1 . A process for producing magnesia, comprising:
 producing magnesium carbonate from a feed material, including:
 subjecting the feed material to dehydroxylation to produce a dehydroxylated material containing magnesium compounds, and 
 contacting a CO2-containing feed gas with the dehydroxylated material to produce a gas-contacted material comprising the magnesium carbonate; and 
   subjecting at least a portion of the magnesium carbonate to calcination to produce a calcined material comprising magnesia;   wherein the CO2-containing feed gas contacted with the dehydroxylated material comprises a recycled CO2 by-product and a CO2-containing emissions stream.   
     
     
         2 . The process of  claim 1 , wherein producing the magnesium carbonate further comprises providing the feed material as part of an aqueous slurry and contacting the CO2-containing feed gas with the aqueous slurry. 
     
     
         3 . The process of  claim 2 , further comprising:
 in the contacting step, producing a carbonate loaded slurry comprising precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates;   separating the carbonate loaded slurry into an aqueous phase comprising the precipitable carbonates and a solid phase;   precipitating the magnesium carbonates from the aqueous phase; and   separating the magnesium carbonates from the aqueous phase;   wherein at least a portion of the separated magnesium carbonates are then supplied to the calcination.   
     
     
         4 . The process of  claim 1 , wherein the CO2-containing emissions stream is supplied directly as produced from a plant to the contacting step with the dehydroxylated material. 
     
     
         5 . The process of  claim 4 , wherein the CO2-containing emissions stream comprises emissions from an emission source that is separate from the process for producing the magnesia. 
     
     
         6 . The process of  claim 1 , wherein the recycled CO2 by-product is derived from the calcination. 
     
     
         7 . The process of  claim 1 , wherein the feed material is a magnesium silicate material. 
     
     
         8 . The process of  claim 1 , wherein the feed material is pre-treated to produce magnesium-containing particulate material prior to carbonation, and the magnesium-containing particulate material has a magnesium content between about 10 wt % and about 35 wt %. 
     
     
         9 . The process of  claim 1 , wherein the feed material is derived from a mining residue comprising phyllosilicate mining residue or chrysotile mining residue. 
     
     
         10 . The process of  claim 1 , further comprising subjecting the magnesium-containing material to size reduction and removal of a magnetic fraction prior to carbonation. 
     
     
         11 . The process of  claim 1 , wherein the CO2 content of the recycled CO2 by-product is at least 20% greater than that of the CO2-containing emissions stream. 
     
     
         12 . A process for producing magnesia, comprising:
 in a carbonation stage, producing magnesium carbonate from a feed material, including:
 subjecting the feed material to dehydroxylation to produce a dehydroxylated material containing magnesium compounds, 
 contacting a CO2-containing feed gas with the dehydroxylated material in the form of a slurry to produce a carbonate loaded slurry comprising the magnesium carbonate; 
 separating the carbonate loaded slurry into an aqueous phase comprising precipitable carbonates and a solid phase; and 
 obtaining the magnesium carbonate from the aqueous phase; 
   in a calcination stage, subjecting at least a portion of the magnesium carbonate to calcination to produce magnesia;   wherein producing the magnesium carbonate further includes recycling one or more streams back into the carbonation stage, the one or more streams selected from the group consisting of a recyclable CO2-containing by-product stream generated in the calcination stage, a recyclable CO2-containing by-product generated by the dehydroxylation, a recyclable solid stream obtained from the solid phase, and a recyclable aqueous stream obtained from the aqueous phase.   
     
     
         13 . The process of  claim 12 , wherein the recyclable CO2-containing by-product stream generated in the calcination stage is provided back into the carbonation stage. 
     
     
         14 . The process of  claim 12 , wherein the recyclable CO2-containing by-product generated by the dehydroxylation is provided back into the carbonation stage. 
     
     
         15 . The process of  claim 12 , wherein the recyclable solid stream obtained from the solid phase is provided back into the carbonation stage. 
     
     
         16 . The process of  claim 12 , wherein the recyclable aqueous stream is provided back into the carbonation stage. 
     
     
         17 . A process for producing magnesia, comprising:
 in a carbonation stage, producing magnesium carbonate from a feed material, including:
 subjecting the feed material to dehydroxylation to produce a dehydroxylated material containing magnesium compounds, and 
 contacting a CO2-containing feed gas with the dehydroxylated material to produce a gas-contacted material comprising the magnesium carbonate; and 
   in a calcination stage, subjecting at least a portion of the magnesium carbonate to calcination to produce magnesia;   wherein the CO2-containing feed gas contacted with the dehydroxylated material comprises a recycled CO2 by-product and a CO2-containing emissions stream.   
     
     
         18 . The process of  claim 17 , wherein the carbonation stage comprises contacting of the CO2-containing feed gas with the dehydroxylated material is performed in a slurry to produce a carbonate loaded slurry comprising the magnesium carbonate; separating the carbonate loaded slurry into an aqueous phase comprising precipitable carbonates and a solid phase; and obtaining the magnesium carbonate from the aqueous phase. 
     
     
         19 . The process of  claim 18 , wherein producing the magnesium carbonate further includes recycling a portion of the solid phase back into the carbonation stage to form part of the slurry. 
     
     
         20 . The process of  claim 18 , wherein producing the magnesium carbonate further includes recycling a portion of the aqueous phase back into the carbonation stage to form part of the slurry.